Lighting circuit and vehicle lamp employing same
AssigneeKoito Manufacturing Co., Ltd.
InventorTomoyuki Ichikawa
Life of this patent
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Abstract
A lighting circuit utilizes a buck converter that supplies a drive current to a light source and is feedback-controlled so that the drive current comes close to a target current. An open-circuit detection circuit compares a potential difference between and input voltage and an output voltage of the buck converter with a threshold voltage.
Claims6
A lighting circuit comprising:
- a buck converter which supplies a drive current to a light source and is feedback-controlled so that the drive current comes close to a target current;
- and
- an open-circuit detection circuit which compares a potential difference between an input voltage and an output voltage of the buck converter with a prescribed threshold voltage and which outputs an abnormality detection signal showing an open-circuit abnormality if the potential difference is lower than the prescribed threshold voltage.
The lighting circuit according to claim, wherein the open-circuit detection circuit comprises a positive-negative-positive (pnp) bipolar transistor whose emitter and base are connected to an input terminal and an output terminal of the buck converter, respectively.
Dependencies are inferred from the claim text.